Generally, the amount of moving image data is very large. Therefore, an apparatus that handles moving image data compresses the amount of data by encoding the moving image data, before transmitting the moving image data to other apparatus or storing the moving image data in a storage device. In particular, in order to encode such moving image data at high speed, there is proposed a moving image encoding apparatus which divides the moving image data into a plurality of sub-data, encodes the sub-data in parallel by using a plurality of encoders, and thereafter splices the encoded sub-data into single bitstream data.
When the encoded moving image data is transferred to a decoding apparatus, the decoding apparatus is expected to be able to decode the encoded moving image data. For that purpose, it is postulated that the decoding apparatus includes a buffer having a given capacity for temporarily storing the encoded moving image data. In this case, the moving image data encoding apparatus is requested to encode the moving image data so that the amount of data to be stored in the buffer will always fall within the limits of that capacity. This hypothetical buffer provided in the decoding apparatus will hereinafter be referred to as the standard decoder buffer. For example, in the Moving Picture Experts Group (MPEG), a concept referred to as the Video Buffering Verifier (VBV) is defined to address the variation in the amount of space that the encoded moving image data occupies in the standard decoder buffer. The VBV employs a model in which, after the encoded moving image data in an amount equal to the initial delay has been stored into the standard decoder buffer at the maximum transfer bit rate, data for one picture is removed instantaneously from the standard decoder buffer at predetermined intervals of time. Then, when the moving image data is encoded at a fixed bit rate, the amount of space that the encoded moving image data transferred into the standard decoder buffer occupies in the standard decoder buffer has to be held within the limits defined by the maximum and minimum allowable values of the standard decoder buffer.
However, when a plurality of moving image data blocks separately encoded are spliced together, the bitstream data produced by splicing the moving image data blocks may not satisfy the specification of the standard decoder buffer, though each individual moving image data block may satisfy the specification of the standard decoder buffer. This problem arises for the following reason. That is, it is defined that the bitstream data continue to be transferred into the standard decoder buffer at the maximum transfer bit rate until the transmission of the bitstream data is completed. However, depending on the timing at which two successively transmitted encoded moving image data blocks are spliced, there may arise inconsistency in motion between the amount of restoration of the buffer before the temporally succeeding encoded moving image data block is spliced and the amount of restoration of the buffer when the two encoded moving image data blocks are treated as a continuous moving image data block not divided at the splicing point. As a result, when the last picture in the temporally preceding encoded moving image data block among the two encoded moving image data blocks is decoded, the amount of space that the temporally succeeding encoded moving image data block occupies in the standard decoder buffer does not coincide with the amount of buffer space occupied by the bitstream data.
To address this problem, there is proposed a technique which encodes moving image data so as to satisfy the specification of the standard decoder buffer by calculating the amount of initial delay at each splicing point based on the result obtained by simulating the change in the amount of occupancy in the standard decoder buffer. There is also proposed a technique which, after decoding data contained in the splicing section of spliced MPEG image data, re-encodes the data contained in the splicing section in such a manner that the amount of occupancy in the standard decoder buffer falls within the limits defined by the maximum and minimum allowable values of the buffer.    Patent document 1: Japanese Unexamined Patent Publication No. 2008-85673    Patent document 2: Japanese Unexamined Patent Publication No. 2004-297829